Liquid crystal lens have been proposed over the years for selectively controlling the index of refraction of light passing through the lens. See for example, U.S. Pat. No. 4,572,616 to Kowel; and Sato, Liquid Crystal Lens-Cells with Variable Focal Length, Japanese Journal of Applied Physics, Vol. 18, No. 9, September 1979, pp. 1679-1684. However, there have been problems with using the liquid crystals. Many of these devices require the liquid crystal material be aligned on convex curved substrates or concave curved substrates, where it is extremely difficult to align the liquid crystal molecules on the curved substrates. Additionally, most of these devices require linearly polarized light sources in order to operate.
In addition other types of devices also require the limitation of using linearized light sources along with other required features such as strip line electrodes. See also for example, Riza and DeJule, Three-terminal adaptive nematic liquid-crystal lens device, Optical Society of America, Vol. 19, No. 14 Optics Letters, Jul. 15, 1994, pp. 1013-1015.
Other types of liquid crystal lens require other features to work. Masuda et al., Liquid-crystal micro lens with a beam-steering function, Applied Optics, Vol. 36, No. 20, Jul. 10, 1997, pp. 4772-4778. requires the use of two polarizers to work as a micro lens.
Several other types of devices have been proposed for tunable liquid crystal lens. U.S. Pat. Nos. 4,907,860 to Noble and 5,299,289 to Omae et al.; 5,764,317 to Sadovnik et al.; 6,061,107 to Yang et al. and 6,072,107 to Komura each describe conventional homogeneous liquid crystal droplets for use as a display panel and not as a tunable lens. U.S. Pat. Nos.: 6,184,954 and 6,246,456 and application 2001/0017675 to Inoue et al. describe other device having homogeneous liquid crystal droplets with no teaching for gradient distribution.
U.S. Pat. No. 6,221,443 to Kubota describes liquid crystal displays having droplets of substantially similar shapes and sizes, that are also not selected to be inhomogeneous. U.S. Pat. No. 6,218,679 to Takahara et al. describes homogeneous liquid crystal droplets that are much smaller than the wavelength of the incident light, and therefore do not scatter light and are transparent to visible light.
U.S. Pat. No. 6,215,535 to Nakajima et al. describes systems using liquid crystal droplets with distorted shapes, which result in scattering light and not focusing, diffracting nor deflecting light as needed with a lens.
U.S. Pat. No. 6,331,881 to Hatano et al. describes the fabrication method of a composite layer, including a resin and a cholesteric liquid crystal material. The resin wall takes the form of pillars or columns. Cholesteric liquid crystal reflects wavelength in the visible range. The formed structure is very different from the inhomogeneous nano-scaled PDLC droplets.